Methods and devices for operating an internal combustion engine having exhaust-gas recirculation are well-known. In this context, it is also known that a cooling device can be provided in an exhaust-gas recirculation line for cooling the recirculated exhaust gas. Since the cooling device in the exhaust-gas recirculation line has an effect on the exhaust-gas emissions of the internal combustion engine, the legislature requires, in the case in which the internal combustion engine drives a vehicle, that the cooling function of the cooling device be monitored within the scope of an on-board diagnosis. Above all, the monitoring is necessary in order that the American OBDII limit values for exhaust-gas emissions can be satisfied.
German Patent No. 100 03 060 describes a monitoring function, which evaluates the dynamic response of temperature sensors in the time and frequency ranges on the basis of control actions of an exhaust-gas recirculation valve. In this context, it is problematic that extreme control actions of the exhaust-gas recirculation valve can lead to undesired torque changes and additional pollution from emissions. Since the inertia of the temperature sensors causes the action to last relatively long, during this time complex coordination is necessary between other operating modes, such as NOx-catalyst regeneration, etc., which also act on the exhaust-gas recirculation valve.